The present invention relates to a containment enclosure for enclosing a cryogenic unit. The containment enclosure has particular application in off-shore locations.
There are many applications which use a cryogenic unit. Such cryogenic units typically include air separation units, gas liquefaction units, and synthesis units. It is sometimes desirable or necessary for reasons of safety to enclose such units, particularly to contain any cryogenic liquids or vapours leaking from the cryogenic unit. Whilst containment enclosures can be desirable in particular in on-shore applications, they are essential in off-shore applications as human operators often have to work and live within a few metres of the cryogenic unit. In many off-shore applications, such as deep sea oil rigs or other platforms and on sea-going vessels, because of the close proximity of the human operators to the cryogenic unit and also because of the difficulties in evacuating human operators from such off-shore applications, containing leaks from a cryogenic unit is of paramount importance.
When a cryogenic liquid or vapour does leak from a cryogenic unit, it is necessary to dispose of or disperse the leaking liquid and/or vapour. In on-shore applications, this can normally simply be achieved by venting the cryogenic liquid and/or vapour to atmosphere. However, venting a cryogenic liquid or vapour to atmosphere can generate a thick fog in the vicinity of the vent, which seriously reduces the visibility in the region of the vent, and can cause icing of neighbouring structures. Moreover, simply venting liquids and vapours to atmosphere can cause a health hazard to human operators working nearby and can cause damage to neighbouring structures, depending on the liquids or vapours which are being vented. For example, where the liquid or vapour is oxygen-rich, there may be a risk of fire or explosion. There is also a risk of structural damage to the carbon steels which are tonically employed in the construction of off-shore rigs by embrittlement fatigue from contact with cryogenic fluids.
In a paper entitled xe2x80x9cTonnage Nitrogen Generation For Oil And Gas Enhanced Recovery In The North Seaxe2x80x9d presented in the Annual Report, Session 6 of the 9th Continental Meeting of the Gas Processors Association, 14th May 1992, there is disclosed a containment enclosure for an air separation unit. The containment enclosure disclosed in that paper utilises a known type of thermal insulation in which loose insulation contained by a wire mesh (xe2x80x9cchicken wirexe2x80x9d) forms a thermally insulating layer which is resistant to penetration of cryogenic leaks from the air separation unit. However, the efficiency of the thermal insulation provided by a loose fill of insulation has been found to be very variable as it is difficult to ensure an optimum and consistent density and hence provide minimum thermal conductivity of the loosely filled insulation. Furthermore, the loosely filled insulation is only merely resistant to cryogenic leaks and severe leaks can penetrate the insulation thereby destroying the integrity and effectiveness of the thermal insulation.
Moreover, where maintenance of a cryogenic unit is required, it is necessary to provide some access through any thermal insulation to the cryogenic unit. In an off-shore application, it is especially important to be able to have easy access to the cryogenic unit for maintenance purposes because any delays in providing maintenance access to the cryogenic unit may increase the safety risk to operators. The removal and addition of any loose filled insulation around a cryogenic unit can be very time-consuming and should preferably therefore be avoided particularly in off-shore applications.
In the containment enclosure disclosed in the paper mentioned above, the containment enclosure has a sump at its base which can receive and contain a liquid leaking from the cryogenic unit contained in the containment enclosure. The sump has a stainless steel liner forming the sump wall. In this prior art proposal, liquid can be passed from the sump to a vaporiser which then vaporises the liquid prior to dispersal.
An object of the present invention is to overcome one or more of the problems mentioned above.
U.S. Pat. No. 4,513,550 discloses a method of building a large-scale tank or reservoir for storing a liquid at low temperature.
U.S. Pat. No. 4,452,162 discloses a corner structure for a cryogenic insulation system used as a large-scale container for storage of cryogenic liquefied gases.
U.S. Pat. No. 4,041,722 discloses a large-scale tank for storage of cryogenic liquefied gases.
DE-A-4038131 and U.S. Pat. No. 4,625,753 each disclose an example of a small-scale container for storage of cryogenic liquefied gases.
According to a first aspect of the present invention, there is provided in combination, a containment enclosure and a cryogenic unit, the cryogenic unit being at least one of an air separation unit, a gas liquefaction unit, a gas synthesis unit, and a gas purification unit, the containment enclosure being arranged to contain liquid leaking from the cryogenic unit and comprising a chamber in which the cryogenic unit is located; a chamber wall which includes thermal insulation for thermally insulating the cryogenic unit in the chamber; and, a sump for receiving liquid leaking from the cryogenic unit; characterised in that: the chamber wall is impermeable to liquid leaking from the cryogenic unit.
The containment enclosure can completely contain all leaks from the cryogenic unit located within the chamber. The integrity of the thermal insulation is maintained at all times.
The chamber wall preferably includes a plurality of thermally insulating bricks for thermally insulating the chamber. The bricks are preferably free of any binder. The bricks are most preferably pre-compressed mineral fibre.
The use of thermally insulating bricks rather than a loose fill thermal insulation as in the prior art greatly facilitates assembly of the containment enclosure and also facilitates access to a cryogenic unit within the chamber for maintenance purposes. The thermal insulation Properties of the bricks can be well defined and will usually be within a very narrow range, which is in contrast to the very variable thermal insulation properties of loose filled thermal insulation. It will be appreciated that the word xe2x80x9cbrickxe2x80x9d used herein includes other substantially self-supporting structures such as, for example, blocks and slabs. It is preferred that the bricks be free of any binder in case any oxygen-containing liquid or vapour leaking from the cryogenic unit does come into contact with the bricks as such binders may have a potential to combust on contact with liquids or vapours containing oxygen.
The bricks are preferably arranged in layers, each layer comprising a plurality of bricks, the bricks in at least one layer being staggered relative to the bricks in an adjacent layer such that the abutment between adjacent bricks in said at least one layer is discontinuous with the abutment between adjacent bricks in said adjacent layer. Staggering the bricks in one layer relative to the bricks in an adjacent layer improves the thermal insulation properties of the bricks as it limits the convection pathways for warm air to enter the chamber from outside the containment enclosure.
A convection break is preferably positioned between at least some bricks. The or each convection break may comprise a sheet of substantially gas-impermeable foil.
In a preferred embodiment, studs or pins are provided for securing the bricks to the chamber wall. The studs can be used to locate the bricks relative to the chamber wall and to each other. The studs can be used, in association with an impermeable panel, to compress the bricks if desired, which may be desirable in order to obtain optimum thermal insulation from the bricks.
At least one panel is preferably affixed to the chamber wall between the insulation and the chamber, said at least one panel being impermeable to liquid leaking from the cryogenic unit to render the chamber wall impermeable to liquid leaking from the cryogenic unit. In a preferred embodiment, a plurality of panels is affixed to the chamber wall between the insulation and the chamber, wherein, at a horizontal connection between adjacent upper and lower panels, the lowermost edge of the upper panel overlies the uppermost edge of the adjacent lower panel on the chamber side of said adjacent upper and lower panels. Preferably, at a vertical connection between adjacent plural panels, the adjoining edges of said adjacent panels are interlocked.
The or each panel is preferably of a material which is such as to prevent any liquids or vapours escaping into the chamber from the cryogenic unit from reaching the insulation. The panel or panels therefore provide a shield or protective layer for the insulation. In the preferred embodiment, plural panels are effectively tiled in a manner similar to roof tiles such that a liquid striking and running down the panels is shed by the panels and does not penetrate into the insulation.
The or at least some of the panels are preferably affixed to and compress the thermal insulation by means of studs which pass through said panels into said insulation. The studs may be fixed at one end to an enclosure wall of the enclosure so that the thermal insulation is compressible between said panels and said enclosure wall.
The sump is preferably open at its uppermost end to receive liquid leaking from the cryogenic unit, the sump being defined by a sump wall and a sump base, and comprising withdrawing means for withdrawing liquid from the sump through the open uppermost end of the sump. The withdrawing means normally requires the specific application of energy (for example electrical power/steam/motive gas) to provide a lift capability for withdrawing liquid. Release of the contained cryogen cannot be achieved by accident as the withdrawing means is remotely energised and can only by achieved by operation of the withdrawing means. A vaporiser may be connected to the withdrawing means for receiving and vaporising liquid withdrawn from the sump. Heating means for heating vapour produced by the vaporiser prior to dispersal of said vapour may be provided. The sump is preferably large enough to contain the whole inventory of the cryogenic unit.
The chamber may have at least one side wall which includes a plurality of insulating bricks for thermally insulating the chamber.
The chamber may have a top wall which includes a plurality of insulating bricks for thermally insulating the chamber.
According to a second aspect of the present invention, there is provided in combination, a containment enclosure and a cryogenic unit, the containment enclosure comprising a chamber in which the cryogenic unit is located, the chamber having a chamber wall which includes a plurality of thermally insulating bricks for thermally insulating the chamber.
The bricks are preferably arranged in layers, each layer comprising a plurality of bricks, the bricks in at least one layer being staggered relative to the bricks in an adjacent layer such that the abutment between adjacent bricks in said at least one layer is discontinuous with the abutment between adjacent bricks in said adjacent layer.
There may be a convection break between at least some bricks.
Preferably, at least one panel is affixed to the chamber wall between the bricks and the chamber to render the bricks impermeable to liquid leaking from the cryogenic unit. A plurality of panels may be affixed to the chamber wall between the bricks and the chamber, wherein, at a horizontal connection between adjacent upper and lower panels, the lowermost edge of the upper panel overlies the uppermost edge of the adjacent lower panel on the chamber side of said adjacent upper and lower panels. A plurality of panels may be affixed to the chamber wall between the bricks and the chamber, wherein, at a vertical connection between adjacent panels, the adjoining edges of said adjacent panels are interlocked.
A sump may be provided for receiving liquid leaking from the cryogenic unit, the sump being open at its uppermost end to receive liquid leaking from the cryogenic unit, the sump being defined by a sump wall and a sump base, the enclosure comprising withdrawing means for withdrawing liquid from the sump through the open uppermost end of the sump. There may be a vaporiser connected to the withdrawing means for receiving and vaporising liquid withdrawn from the sump. Heating means may be provided for heating vapour produced by the vaporiser prior to dispersal of said vapour.
Where panels are provided, the bottom edge of the panels can project beyond the upper lip of the sump to shed liquid without permitting penetration through the insulation behind.
According to a third aspect of the present invention, there is provided in combination, a containment enclosure and a cryogenic unit, the containment enclosure comprising a chamber in which the cryogenic unit is located; a chamber wall which includes thermal insulation for thermally insulating the cryogenic unit in the chamber; a sump for receiving liquid leaking from the cryogenic unit, the sump being open at its uppermost end to receive liquid leaking from the cryogenic unit, the sump being defined by a sump wall and a sump base; and, withdrawing means for withdrawing liquid from the sump through the open uppermost end of the sump.
A vaporiser may be connected to the withdrawing means for receiving and vaporising liquid withdrawn from the sump. Heating means for heating vapour produced by the vaporiser prior to dispersal of said vapour may be provided.
In a preferred embodiment, the sump comprises a sealed membrane of stainless steel or aluminium supported by a floor and walls of glass foam blocks sandwiched between the membrane and the carbon steel outer surface of the enclosure. The foam glass blocks are preferably multi-layered and staggered to avoid continuous abutments through the wall and are laid without adhesive to allow for thermal movement. The faces of adjoining blocks may have a woven glass fibre blanket layer to prevent abrasion of the blocks.
The combination may be situated in an off-shore location.
The cryogenic unit may be an air separation unit or a gas liquefaction unit or a purification or separation unit for other gases.